Windows Universal App中的ComboBox綁定

Question

在我的Windows通用項目中，我有ComboBoxes用於輸入時間。 我的ViewModel中的Hour，Minute和Second屬性綁定了三個組合框...

<StackPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center">
    <ComboBox SelectedItem="{Binding Hour, Mode=TwoWay}" ItemsSource="{Binding HourList}"></ComboBox>
    <ComboBox SelectedItem="{Binding Minute, Mode=TwoWay}" ItemsSource="{Binding MinuteList}"></ComboBox>
    <ComboBox SelectedItem="{Binding Second, Mode=TwoWay}" ItemsSource="{Binding SecondList}"></ComboBox>
</StackPanel>

這是我的ViewModel ...（請注意，我最終希望表單如何同時設置和顯示“ Time”屬性）。

public class TimeEntryViewModel : INotifyPropertyChanged
{
    public bool Accept { get; set; }

    public TimeEntryViewModel(DateTime time)
    {
        Time = time;
        HourList = new ObservableCollection<string> { "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23" };
        MinuteList = new ObservableCollection<string> { "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59" };
        SecondList = new ObservableCollection<string> { "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59" };
    }

    public ObservableCollection<string> HourList { get; set; }
    public ObservableCollection<string> MinuteList { get; set; }
    public ObservableCollection<string> SecondList { get; set; }

    private string _hour;
    public string Hour {
        get { return _hour; }
        set
        {
            _hour = value;
            OnPropertyChanged("Hour");
        }
    }

    private string _minute;
    public string Minute
    {
        get { return _minute; }
        set
        {
            _minute = value;
            OnPropertyChanged("Minute");
        }
    }
    private string _second;
    public string Second
    {
        get { return _second; }
        set
        {
            _second = value;
            OnPropertyChanged("Second");
        }
    }

    public DateTime Time
    {
        get
        {
            return new DateTime(DateTime.Now.Year, 
                DateTime.Now.Month, 
                DateTime.Now.Day, 
                int.Parse(_hour), int.Parse(_minute), int.Parse(_second));
        }
        set
        {
            Hour = value.Hour.ToString("00");
            Minute = value.Minute.ToString("00");
            Second = value.Second.ToString("00");
        }
    }

    #region INotifyPropertyChanged Members

    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    #endregion
}

問題是，即使我在ViewModel上設置了有效的時間，當我第一次顯示頁面時，組合框也不會像我期望的那樣自動選擇小時，分鍾和秒。 它們只是沒有顯示任何值，當我將其放下時，沒有選擇任何項目。 我嘗試改為使ObservableCollections int為基礎，但結果相同。 我在這里想念什么？

Answer 1

這里的問題是在設置ItemsSource之前先設置SelectedItem 。 您可能會認為這並不重要，但不幸的是，它確實如此。 在此說明原因。

將您的代碼更改為：

<StackPanel Orientation="Horizontal"
            HorizontalAlignment="Center"
            VerticalAlignment="Center">
    <ComboBox ItemsSource="{Binding HourList}"
              SelectedItem="{Binding Hour, Mode=TwoWay}"></ComboBox>
    <ComboBox ItemsSource="{Binding MinuteList}"
              SelectedItem="{Binding Minute, Mode=TwoWay}"></ComboBox>
    <ComboBox ItemsSource="{Binding SecondList}"
              SelectedItem="{Binding Second, Mode=TwoWay}"></ComboBox>
</StackPanel>

Answer 2

初始化ObservableCollections后，嘗試設置Time 。 我認為這是因為設置Time ComboBox中沒有任何內容。